Lubricating oil composition for refrigerating machines

ABSTRACT

A lubricating oil composition for refrigerating machines contains a base oil and an additive in a form of a naphthalimide compound. A refrigerant used in a refrigerating machine in which the composition is used is unsaturated hydrofluorocarbon (unsaturated HFC) having a GWP of 1000 or less. When the present lubricating oil composition for refrigerating machines is used in refrigerating equipment such as an open-type automobile air-conditioner, an electric automobile air-conditioner, a gas heat pump, other air-conditioning equipment, a refrigerating machine, a vending machine, a showcase, a water-heating system and a refrigerating/heating system, it is possible to detect the leakage of a refrigerant with a long-lasting stability. Therefore, when an unsaturated fron refrigerant with a poor stability is used in the above-listed equipment, the present lubricating oil composition for refrigerating machines is significantly advantageous.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition forrefrigerating machines.

BACKGROUND ART

Air-conditioner systems and cooling systems use a variety ofrefrigerants, which are likely to leak outside during use. In such acase, a refrigerant-leakage spot needs to be found. Typically, theleakage of the refrigerant is detected simply depending on the presenceor absence of bubbles formed of soapy water sprayed onto pipes andjoints in the system. These days, a leakage-detecting method using afluorescent agent has been developed and a refrigerant-leakage-detectingfluorescent agent is sometimes provided in a receiver dryer in arefrigeration cycle in an automobile air-conditioner.

According to Patent Literatures 1 and 2, a fluorescence dye containing apolycyclic aromatic compound such as xanthene and perylene is used in acooling system to detect the leakage of a refrigerant.

CITATION LIST Patent Literature(s)

Patent Literature 1: JP-A-61-211391

Patent Literature 2: JP-A-2006-52938

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

It should be noted that a refrigerant usable in an air-conditionersystem or a cooling system is a compound having an effect on globalwarming and thus a new refrigerant with a low global warming potential(GWP) has been sought. Examples of increasingly used refrigerants are: arefrigerant (unsaturated chlorofluorocarbon refrigerant) that has anunsaturated carbon-carbon bond in a molecule (e.g., R1234yf); and arefrigerant with a low global warming potential that contributes toreduction in system capacity (e.g., R32).

However, it has been found that typical fluorescent agents as disclosedin Patent Literatures 1 and 2 lower the thermal stability and chemicalstability of a refrigerant oil when used in a system using a refrigerantwith a low global warming potential.

An object of the invention is to provide a lubricating oil compositionfor refrigerating machines that exhibits thermal stability and chemicalstability equal to or more than those of a typical refrigerant oilirrespective of the use of a refrigerant-leakage-detecting fluorescentagent.

Means for Solving the Problems

In order to solve the above problems, according to an aspect of theinvention, the following lubricating oil composition for refrigeratingmachines is provided.

[1] A lubricating oil composition for refrigerating machines contains: abase oil; and an additive in a form of a naphthalimide compound, inwhich a refrigerant used in a refrigerating machine in which thecomposition is used is unsaturated hydrofluorocarbon (unsaturated HFC)having a GWP of 1000 or less.

[2] In the above aspect, the HFC having the GWP of 1000 or less isunsaturated HFC having 3 carbon atoms.

[3] In the above aspect, a blending amount of the naphthalimide compoundis in a range from 0.1 mass % to 10 mass % of a total amount of thecomposition.

[4] In the above aspect, the refrigerant used in the refrigeratingmachine further contains at least one of saturated hydrofluorocarbon(saturated HFC), carbon dioxide (CO₂), hydrocarbon (HC) having 5 or lesscarbon atoms, ammonia, and a fluorine-containing organic compoundrepresented by the following molecular formula (A).

C_(p)O_(q)F_(r)R_(s)  (A)

In the formula: R represents Cl, Br, I or hydrogen; p is an integer of 1to 6; q is an integer of 0 to 2; r is an integer of I to 14; and s is aninteger of 0 to 13 with the proviso that when q is 0, p is an integer of2 to 6 and one or more unsaturated carbon-carbon bonds are contained ina molecule.

[5] In the above aspect, the base oil contains at least one compoundselected from among alkylbenzene, alkylnaphthalene, poly-alpha-olefin,polyvinylether, polyalkylene glycol, polycarbonate, polyol ester and anether compound represented by the following formula (1).

Ra—[(ORb)n—(B)—(ORc)k] x—Rd  (1)

In the formula: Ra and Rd each represent a hydrogen atom, an alkyl grouphaving 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms,or a hydrocarbon group having 2 to 6 bonds and having 1 to 10 carbonatoms; Rb and Rc each represent an alkylene group having 2 to 4 carbonatoms; n and k each are an integer of 0 to 20; x is an integer of 1 to6; and (B) represents a polymer portion having 3 or more monomer unitsrepresented by the following formula (2).

In the formula: R⁴, R⁵ and R⁶ each represent a hydrogen atom or ahydrocarbon group having 1 to 8 carbon atoms and are mutually the sameor different; R⁷ represents a divalent hydrocarbon group having 1 to 10carbon atoms or a divalent ether-bonded oxygen-containing hydrocarbongroup having 2 to 20 carbon atoms; Rx represents a hydrogen atom or ahydrocarbon group having 1 to 20 carbon atoms; m is a number with anaverage of 0 to 10 and plural m are mutually the same or different ineach unit; R⁴ to R⁸ are mutually the same or different in each unit;plural R⁷O are mutually the same or different; and m in the formula (2)is an integer of 1 or more when k and n in the formula (1) are both 0.

[6] In the above aspect, the lubricating oil composition forrefrigerating machines has a kinematic viscosity at 100 degrees C. in arange from 1 mm²/s to 50 mm²/s.

[7] In the above aspect, the base oil contains at least another additiveselected from among an extreme pressure agent, an oiliness agent, anantioxidant, an acid scavenger, a metal deactivator and an antifoamingagent.

[8] In the above aspect, the lubricating oil composition forrefrigerating machines is used in refrigerating equipment such as anopen-type automobile air-conditioner, an electric automobileair-conditioner, a gas heat pump, other air-conditioning equipment, arefrigerating machine, a vending machine, a showcase, a water-heatingsystem and a refrigerating/heating system.

The lubricating oil composition for refrigerating machines according tothe above aspect can be thermally and chemically stable under anatmosphere of various refrigerants and thus a leakage-detectingperformance can be exhibited for a long time. Therefore, the lubricatingoil composition according to the above aspect is favorably usable in arefrigerating machine that uses an unstable refrigerant having anunsaturated bond.

DESCRIPTION OF EMBODIMENT(S)

A lubricating oil composition for refrigerating machines according to anexemplary embodiment of the present invention (hereinafter, also simplyreferred to as “the present composition”) is a lubricating oilcomposition for refrigerating machines provided by blending a base oilwith an additive in a form of a naphthalimide compound. The exemplaryembodiment will be described below in detail.

The base oil may be a mineral oil or a synthetic base oil. The syntheticbase oil is preferably at least one selected from among, for instance,alkylbenzene (AB), alkylnaphthalene (AN), poly-alpha-olefin (PAO),polyvinylether (PVE), polyalkylene glycol (PAG), polycarbonate (PC),polyol ester (POE) and an ether compound (ECP) represented by the aboveformula (1).

The above base oils will be first described below.

(1) Mineral Oil

The mineral oil is preferably a so-called highly purified mineral oil,examples of which are: a purified oil obtained by atmosphericdistillation of a paraffin-base crude oil, an intermediate-base crudeoil or a naphthene-base crude oil or by ordinarily purifying adistillate oil obtained by vacuum distillation of a residual oil leftafter atmospheric distillation; a deeply dewaxed oil obtained byperforming deep dewaxing after purification; and a hydrotreated oilobtained by hydrotreatment. The purification method is not particularlylimited and thus a variety of methods are usable.

(2) Alkylbenzene (AB)

Any alkylbenzene for a refrigerant oil may be usable, but, in terms ofthermal stability, alkylbenzene (including monoalkylbenzene,dialkylbenzene and trialkylbenzene) having 20 or more carbon atoms in analkyl group in total (when plural alkyl groups exist, the sum of carbonatoms in the alkyl groups) is preferable and alkylbenzene having 20 ormore carbon atoms in total and having two or more alkyl groups (e.g.,dialkylbenzene) is more preferable.

(3) Alkylnaphthalene (AN)

As the alkylnaphthalene according to the exemplary embodiment,alkylnaphthalene having a naphthalene ring bonded with two or threealkyl groups is favorably usable. In particular, the alkylnaphthalenefurther preferably has 20 or more carbon atoms in total in terms ofthermal stability. According to the exemplary embodiment, one of suchalkylnaphthalenes may be singularly used or, alternatively, a mixture oftwo or more thereof may be used.

(4) Poly-alpha-olefin (PAO)

As the poly-alpha-olefin according to the exemplary embodiment, avariety of poly-alpha-olefins are usable but an alpha-olefin polymerhaving 8 to 18 carbon atoms is typically used. Preferable examples ofsuch a polymer are a 1-dodecene polymer, a 1-decene polymer and a1-octene polymer in terms of thermal stability and lubricity. Among theabove, a 1-decene polymer is preferable. Incidentally, according to theexemplary embodiment, the poly-alpha-olefin is preferably hydrotreatedin terms of thermal stability. One of such poly-alpha-olefins may besingularly used or, alternatively, a mixture of two or more thereof maybe used.

(5) Polyvinylether (PVE)

The polyvinylether usable as the base oil includes: polyvinyletherobtained by polymerizing vinylether monomers (hereinafter referred to aspolyvinylether I) and polyvinylether obtained by co-polymerizingvinylether monomers and hydrocarbon monomers having an olefindouble-bond (hereinafter referred to as polyvinylether copolymer II).

Examples of the vinylether monomer usable as a material of thepolyvinylether I are vinylmethylether, vinylethylether,vinyl-n-propylether and vinyl-isopropylether. These vinylether monomerscan be prepared by a known method.

Examples of the vinylether monomer usable as a material of thepolyvinylether copolymer II are the same as those of the vinylethermonomer for the polyvinylether I) and one of the examples may besingularly used or, alternatively, two or more thereof may be used incombination. Examples of the hydrocarbon monomer having an olefindouble-bond (i.e., the other material of the polyvinylether copolymerII) are ethylene, propylene, butenes, pentenes, hexenes, heptenes,octenes, diosobutylene, triisobutylene, styrene, alpha-methyl styreneand alkyl-substituted styrenes. In particular, polyethylvinylether,polyisobutylvinylether and a copolymer of polyethylvinylether andpolyisobutylvinylether are preferable.

(6) Polyalkylene Glycol (PAG)

According to the exemplary embodiment, the polyalkylene glycol usable asthe base oil is, for instance, a compound represented by the followingformula (3).

R⁹-[(OR¹⁰)_(m1)—OR¹¹]_(n1)  (3)

In the formula: R⁹ represents a hydrogen atom, an alkyl group having 1to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms or analiphatic hydrocarbon group having 2 to 6 bonds and having 1 to 10carbon atoms; R¹⁰ represents an alkylene group having 2 to 4 carbonatoms; R¹¹ represents a hydrogen atom, an alkyl group having 10 1 to 10carbon atoms or an acyl group having 2 to 10 carbon atoms; n1 is aninteger of 1 to 6; and m1 is a number with an average of m1×n1 beingwithin a range from 6 to 80.

Such polyalkylene glycols are favorably, for instance, polyoxypropyleneglycol dimethyl ether, polyoxypropylene glycol monomethyl ether,poly(oxyethylene)(oxypropylene) glycol dimethyl ether,poly(oxyethylene)(oxypropylene) glycol monomethyl ether,polyoxypropylene glycol monobutyl ether and polypropylene glycoldiacetate in terms of economic efficiency and effects.

(7) Polycarbonate (PC)

For the present composition, the polycarbonate compound usable as thebase oil may be polycarbonate having two or more carbonate bonds in onemolecule. Specifically, the polycarbonate compound may preferably be atleast one selected from among (i) a compound represented by thefollowing formula (4) and (ii) a compound represented by the followingformula (5).

In the formula: Z represents a residue obtained by removing a hydroxylgroup from a c-valent alcohol having 1 to 12 carbon atoms; R¹²represents a linear or branched alkylene group having 2 to 10 carbonatoms; ^(R′3) represents a monovalent hydrocarbon group having 1 to 12carbon atoms or a group having an ether bond represented byR¹⁵(O—R¹⁴)d—, in which R¹⁵ represents a hydrogen atom or a monovalenthydrocarbon group having 1 to 12 carbon atoms, R¹⁴ represents a linearor branched alkylene group having 2 to 10 carbon atoms, and d is aninteger of I to 20; a is an integer of 1 of 30; b is an integer of 1 to50; and c is an integer of 1 to 6.

In the formula, R¹⁶ represents a liner or branched alkylene group having2 to 10 carbon atoms, e is an integer of 1 to 20, and Z, R¹², R¹³, a, band c are defined to be the same as above.

In the formulae (4) and (5), Z is a residue obtained by removing ahydroxyl group from any one of mono- to hexa-valent alcohols having 1 to12 carbon atoms, and is particularly preferably a residue obtained byremoving a hydroxyl group from a monovalent alcohol having 1 to 12carbon atoms.

(8) Polyol Ester (POE)

For the present composition, the polyol ester compound usable as thebase oil is preferably an ester of a diol or a polyol havingapproximately 3 to 20 hydroxyl groups and a fatty acid havingapproximately 1 to 24 carbon atoms. In terms of hydrolytic stability, apolyol is particularly preferable, an ester of neopentyl glycol,trimethylolethane, trimethylolpropane, trimethylolbutane orpentaerythritol is more preferable, and an ester of pentaerythritol isthe most preferable due to its particularly excellent compatibility withthe refrigerant and hydrolytic stability.

In terms of lubricity, the fatty acid preferably has 3 or more carbonatoms, more preferably has 4 or more carbon atoms, further morepreferably 5 or more carbon atoms, and most preferably has 10 or morecarbon atoms. Further, in terms of compatibility with the refrigerant,the fatty acid preferably has 18 or less carbon atoms, more preferablyhas 12 or less carbon atoms, and most preferably has 9 or less carbonatoms. The fatty acid may be a linear or branched. While beingpreferably linear in terms of lubricity, the fatty acid is preferablybranched in terms of hydrolytic stability. The fatty acid may besaturated or unsaturated. In particular, pentaerythritol octanoic acidnonanoic acid ester is preferable.

(9) Ether Compound

For the present composition, for instance, an ether compound having astructure represented by the following formula (1) is preferable as thebase oil.

Ra—[(ORb)n—(B)—(ORc)k]—Rd  (1)

In the formula: Ra and Rd each represent a hydrogen atom, an alkyl grouphaving 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms,or a hydrocarbon group having 2 to 6 bonds and having 1 to 10 carbonatoms; Rb and Re each represent an alkylene group having 2 to 4 carbonatoms; n and k each are an integer of 0 to 20; x is an integer of 1 to6; and (B) represents a polymer portion having 3 or more monomer unitsrepresented by the following formula (2).

In the formula (2), R⁴, R⁵ and R⁶ each represent a hydrogen atom or ahydrocarbon group having 1 to 8 carbon atoms and may be mutually thesame or different. R⁷ represents a divalent hydrocarbon group having 1to 10 carbon atoms or a divalent ether-bonded oxygen-containinghydrocarbon group having 2 to 20 carbon atoms. R⁸ represents a hydrogenatom or a hydrocarbon group having 1 to 20 carbon atoms. m is a numberwith an average of 0 to 10 and plural in are mutually the same ordifferent in each unit. R⁴ to R⁸ are mutually the same or different ineach unit. Plural R⁷O are mutually the same or different. m in theformula (2) is an integer of 1 or more when k and n in the formula (1)are both 0.

The above ether compound may be prepared by polymerizing vinyl ethermonomers using one of alkylene glycol, polyalkylene glycol and amonoether of alkylene glycol or polyalkylene glycol as an initiator.

The ether compound preferably has a terminal structure as follows.Specifically, in terms of stability of synthesis reaction, the ethercompound preferably has a structure of the formula (1), in which Ra is ahydrogen atom, n is 0, Rd (the other end) is hydrogen atom, and k is 0.In particular, a copolymer of polypropylene glycol andpolyethylvinylether and a copolymer of polyethylene glycol andpolyethylvinylether are preferable.

Regarding the above synthetic base oils (compounds), the molecularweight is preferably in a range from 150 to 5,000 and more preferably ina range from 300 to 3000 in terms of suppression of evaporation, flashpoint, properties required of a refrigerant oil, and the like. Theviscosity index is preferably 60 or more.

According to the exemplary embodiment, one of the above base oils(mineral oils and synthetic base oils) may be singularly used or amixture thereof may be used. In either case, a preferable kinematicviscosity at 100 degrees C. is in a range from 1 mm²/s to 50 mm²/s, morepreferably in a range from 3 mm²/s to 50 mm²/s, further more preferablyin a range from 5 mm²/s to 30 mm²/s, and particularly preferably in arange from 5 mm²/s to 20 mm²/s.

The viscosity index of the base oil of the present composition ispreferably 60 or more, more preferably 80 or more, and further morepreferably 100 or more.

In the present composition, the base oil is blended with an additive ina form of a naphthalimide compound. The additive is hereinafter alsoreferred to as the present additive.

The present additive functions as a leakage detector to detect theleakage of the refrigerant and the present composition from arefrigerating machine (refrigerating system). Specifically, a compoundhaving a conjugated system in a form of a naphthalimide structure emitsfluorescent light in response to ultraviolet ray applied thereto, sothat a leakage spot can be easily found. Further, a system including alubricating oil composition provided by blending the present additiveand a refrigerant is thermally and chemically stable.

The naphthalimide compound is, for instance, a compound having askeleton structure represented by the following formula (6).

In the formula, R¹ and R² are substituents that may be mutually the sameor different, examples of which are saturated hydrocarbon, unsaturatedhydrocarbon and aromatic hydrocarbon. The naphthalimide compound can beobtained as a result of substitution reaction of a4-chloro-1,8-naphthalic anhydride with at least one ether amine, atleast one branched alkyl amine or a mixture of the ether amine and thebranched alkyl amine with the proviso that the resulting productstructurally falls within a range defined by the formula (6). A specificexample is a naphthalimide compound having a structure represented bythe following formula (7) or (8).

The blending amount (added amount) of the naphthalimide compoundrelative to the lubricating oil composition is preferably in a rangefrom 0.001 mass % to 10 mass %, more preferably in a range from 0.001mass % to 5 mass %, further more preferably in a range from 0.001 mass %to 0.5 mass %, and the most preferably in a range from 0.001 mass % to0.1 mass %. When the blending amount falls below the above lower limit,a leakage spot is unlikely to be found due to a small amount offluorescent light emitted in response to the leakage of the presentcomposition from a refrigerating machine. On the other hand, when thenaphthalimide compound is blended in an amount more than the above upperlimit, the performance of the naphthalimide compound as a leakagedetector cannot be especially improved while the stability of thepresent composition may be impaired.

A refrigerant usable with the present composition is unsaturatedhydrofluorocarbon (unsaturated HFC) with a GWP of 1000 or less.Preferable examples of the unsaturated hydrofluorocarbon are a fluorideof a linear or branched chained olefin having 2 to 6 carbon atoms and afluoride of a cyclic olefin having 4 to 6 carbon atoms.

Specific examples of the unsaturated hydrofluorocarbon compound areethylene substituted with 1 to 3 fluorine atoms, propene substitutedwith 1 to 5 fluorine atoms, butenes substituted with 1 to 7 fluorineatoms, pentenes substituted with 1 to 9 fluorine atoms, hexenessubstituted with 1 to 11 fluorine atoms, cyclobutene substituted with 1to 5 fluorine atoms, cyclopentene substituted with 1 to 7 fluorineatoms, and cyclohexene substituted with 1 to 9 fluorine atoms. From theabove-listed substances, the unsaturated HFC with a GWP of 1000 or lessmay be selected.

Among the above-listed unsaturated HFC, unsaturated HFC having 3 carbonatoms is preferable. In particular, a compound represented by C₃HF₃,C₃H₂F₄ or C₃H₃F₃ is preferable due to a low global warming potential.Examples of the propene fluoride are a variety of isomers ofpentafluoropropene, 3,3,3-trifluoropropene, 1,3,3,3-tetrafluoropropeneand 2,3,3,3-tetrafluoropropene, among which 1,3,3,3-tetrafluoropropene(HFO1234ze) and 2,3,3,3-tetrafluoropropene (HFO1234yf) are particularlypreferable considering a low global warming potential.

A combination of a saturated hydrofluorocarbon refrigerant having 1 or 2carbon atoms and an unsaturated hydrofluorocarbon refrigerant having 3carbon atoms is also favorably usable. Examples of such a combinationare a combination of HFO1234yf (mentioned above) and CH₂F (HFC32), acombination of HFO1234ze and HFC32, a combination of HFO1234yf andCHF₂CH₃ (HFC152a), and a combination of HFO1234ze and HFC152a.

When the present composition is used in a refrigerating machine, therefrigerant in the refrigerating machine may further be blended with,for instance, saturated hydrofluorocarbon (saturated HFC), carbondioxide (CO₂), hydrocarbon (HC) having 5 or less carbon atoms, ammonia,and/or a fluorine-containing compound represented by the followingmolecular formula (A).

C_(p)O_(q)F_(r)R_(s)  (A)

In the formula, R represents Cl, Br, I or hydrogen, p is an integer of 1to 6, q is an integer of 0 to 2, r is an integer of 1 to 14, and s is aninteger of 0 to 13. When q is 0, p is an integer of 2 to 6 and one ormore unsaturated carbon-carbon bonds are contained in a molecule.

The saturated HFC is preferably an alkane fluoride having 1 to 4 carbonatoms. In particular, methane or ethane fluorides having 1 or 2 carbonatoms such as trifluoromethane, difluoromethane, 1,1-difluoroethane,1,1,1-trifluoroethane, 1,1,2-trifluoroethane, 1,1,1,2-tetrafluoroethane,1,1,2,2-tetrafluoroethane and 1,1,1,2,2-pentafluoropropane arefavorable.

Next, the refrigerant represented by the molecular formula (A) will bedescribed.

The molecular formula (A), which shows the types and numbers of elementsin the molecule, represents a fluorine-containing organic compound inwhich the number p of carbon atoms C is 1 to 6. Any fluorine-containingorganic compound having 1 to 6 carbon atoms possesses physical andchemical properties such as a boiling point, a freezing point and anevaporative latent heat required of a refrigerant.

In the molecular formula (A), the bonding configurations of p carbonatoms represented by C_(p) include carbon-carbon single bond,unsaturated bond such as carbon-carbon double bond and carbon-oxygendouble bond. Unsaturated carbon-carbon bond is preferably carbon-carbondouble bond in terms of stability. While the number of unsaturatedcarbon-carbon bond is 1 or more, the number is preferably 1.

In the molecular formula (A), the bonding configurations of q oxygenatoms represented by O_(q) are preferably oxygen derived from an ethergroup, a hydroxyl group or a carbonyl group. The number q of oxygenatoms may be 2, which is also true of when two ether groups, hydroxylgroups or the like are contained. On the other hand, when q is 0 (i.e.,no oxygen atom is contained in the molecule), p is in a range from 2 to6 and one or more unsaturated bonds such as carbon-carbon double bondare contained in the molecule. In other words, at least one of thebonding configurations of p carbon atoms represented by C_(p) isrequired to be unsaturated carbon-carbon bond.

In the molecular formula (A), R represents Cl, Br, I or hydrogen. R maybe any one of Cl, Br, I and hydrogen but is preferably hydrogen, whichis less likely to lead to ozone depletion.

As described above, preferable examples of the fluorine-containingorganic compound represented by the molecular formula (A) are anunsaturated hydrofluorocarbon compound, a fluoroether compound, afluoroalcohol compound and a fluoroketone compound.

The present composition may further contain at least one additiveselected from among an extreme pressure agent, an oiliness agent, anantioxidant, an acid scavenger, a metal deactivator and an antifoamingagent as long as an object of the invention is achieved.

Examples of the extreme pressure agent are: phosphorus extreme pressureagents such as phosphate, acid phosphate, phosphite, acid phosphite andamine salts thereof; metal carboxylate; and sulfur extreme pressureagents such as sulfurized fat and oil, sulfurized fatty acid, estersulfide, olefin sulfide, dihydrocarbyl polysulfide, thiocarbamates,thioterpenes and dialkyl thiodipropionates.

The blending amount of the extreme pressure agent is preferably in arange from 0.001 mass % to 10 mass % of the total amount of thecomposition in terms of lubricity and stability.

Examples of the oiliness agent are: aliphatic saturated or unsaturatedmonocarboxylic acids such as stearic acid and oleic acid; polymerizedfatty acids such as dimer acid and hydrogenated dimer acid; hydroxylfatty acid such as ricinoleic acid and 12-hydroxystearic acid; aliphaticsaturated or unsaturated monoalcohols such as lauryl alcohol and oleylalcohol; aliphatic saturated or unsaturated monoamines such asstearylamine and oleylamine; aliphatic saturated or unsaturatedmonocarboxylic acid amides such as lauric acid amide and oleic acidamide; and partial esters of polyhydric alcohols such as glycerin andsorbitol and aliphatic saturated or unsaturated monocarboxylic acids.

The blending amount of the oiliness agent is preferably in a range from0.01 mass % to 10 mass % of the total amount of the composition.

Preferable examples of the antioxidant are phenol antioxidants such as2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol and2,2′-methylenebis(4-methyl-6-tert-butylphenol) and amine antioxidantssuch as phenyl-alpha-naphthylamine and N,N′-diphenyl-p-phenylenediamine.The blending amount of the antioxidant is preferably in a range from0.01 mass % to 5 mass % of the total amount of the composition in termsof effects, economic efficiency and the like.

Examples of the acid scavenger are phenyl glycidyl ether, alkyl glycidylether, alkylene glycol glycidyl ether (e.g., polypropylene glycoldiglycidyl ether), phenyl glycidyl ester, alkyl glycidyl ester,cyclohexene oxide, alpha-olefin oxide, epoxy compounds such asepoxidized soybean oil. Among the above, phenyl glycidyl ether, alkylglycidyl ether, alkylene glycol glycidyl ether, cyclohexene oxide andalpha-olefin oxide are preferable in terms of compatibility.

The blending amount of the acid scavenger is preferably in a range from0.005 mass % to 5 mass % of the total amount of the composition in termsof effects and suppression of generation of sludge.

According to the exemplary embodiment, the stability of the presentcomposition can be improved by blending the acid scavenger. Further,when the above extreme pressure agent and antioxidant are additionallyused, the stability of the composition can be further improved.

An example of the metal deactivator is N-[N′,N′-dialkyl (an alkyl grouphaving 3 to 12 carbon atoms) aminomethyl]tolutriazole. Examples of theantifoaming agent are silicone oil and fluorinated silicone oil.

The kinematic viscosity at 40 degrees C. of the present composition ispreferably in a range from 1 mm²/s to 400 mm²/s, more preferably in arange from 3 mm²/s to 300 mm²/s, and further more preferably in a rangefrom 5 mm²/s to 200 mm²/s.

When a refrigerating machine uses the present composition, theabove-listed refrigerants and the present composition are usedpreferably in a mass ratio of 99/1 to 10/90 (refrigerant/the presentcomposition) and more preferably in a mass ratio of 95/5 to 30/70. Whenthe amount of the refrigerant falls below the above range, therefrigerating performance is unfavorably lowered. When the amount of therefrigerant exceeds the above range, the lubricity is unfavorablylowered.

Examples of a refrigerating machine (refrigerating system) in which thepresent composition is favorably usable are a compressor, a condenser,an expansion mechanism (e.g., capillary tube and expansion valve), arefrigerating system necessarily provided with an evaporator, arefrigerating system provided with an ejector cycle, and a refrigeratingsystem provided with a dryer (desiccant: natural/synthetic zeolite). Thecompressor may be open, semi-hermetic or hermetically sealed and a motorof the hermetically sealed compressor may be an AC motor or a DC motor.A compression method may be rotary compression, scroll compression,swing compression or piston compression. The compressor may be asmall-sized compressor (approximately 0.2 kW) or a large-sizedcompressor (approximately 30 kW).

The amount of water contained in such a refrigerating system ispreferably 500 mass ppm or less and more preferably 300 mass ppm orless. The partial pressure of residual air is preferably 13 kPa or less,more preferably 10 kPa or less, and further more preferably 5 kPa orless.

Since the base oil of the present composition is blended with anadditive in a form of a naphthalimide compound, the thermal stabilityand chemical stability of the lubricating oil composition are notimpaired. Therefore, when the present lubricating oil composition forrefrigerating machines is used in, for instance, an automobileair-conditioner, an electric automobile air-conditioner, a gas heatpump, other air-conditioning equipment, a refrigerating machine, avending machine, a showcase, a water-heating system and a refrigeratingmachine with a refrigerating/heating system, it is possible to detectthe leakage of a refrigerant with a long-term stability. When anunsaturated chlorofluorocarbon refrigerant with a low stability is usedin the above-listed equipment, the present composition is significantlyadvantageous.

EXAMPLE(S)

Next, the exemplary embodiment of the invention will be described infurther detail with reference to Examples, which are by no meansintended to limit the scope of the invention.

Examples 1 to 10 and Comparatives 1 to 10

Lubricating oil compositions were prepared according to formulations asshown in Tables 1 and 2 and the thermal/chemical stability of eachcomposition was evaluated by the following thermal-stability test.Incidentally, lubricating oil compositions to which no leakage detectoris added are shown as References 1 and 2 in Table 1.

Thermal-Stability Test

An autoclave (an inner value: 200 mL) filled with thecomposition/refrigerant (ratio: 30 g/30 g, water content in thecomposition: 500 mass ppm) and a metal catalyst made of iron, copper andaluminum was closed (air: 25 mL) and left under the conditions of atemperature of 175 degrees C. for 168 hours. An acid value was thenmeasured. Incidentally, the acid value was measured by an electricalpotential technique in accordance with “Determination of LubricantNeutralization Number” defined by JIS K2501.

HFO1234yf (2,3,3,3-tetrafluoropropene) was used as the refrigerant.

TABLE 1 Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ref. Ref. 1 2 3 4 5 6 78 9 10 1 2 Formulation Base PAG 94.299 94.200 89.300 84.300 — — — — — —97.300 94.300 (mass %) Oil PVE — — — — 94.299 93.800 89.300 84.300 — — —— ECP — — — — — — — — 93.300 — — — POE — — — — — — — — — 93.800 — —Leakage Detector 1 0.001 0.100 5.000 10.000 0.001 0.500 5.000 10.0000.500 0.500 — — Acid Scavenger 3.000 3.000 3.000 3.000 3.000 3.000 3.0003.000 3.000 3.000 1.000 3.000 Oxygen Scavenger 1.000 1.000 1.000 1.0001.000 1.000 1.000 1.000 1.000 1.000 — 1.000 Other Additives 1.700 1.7001.700 1.700 1.700 1.700 1.700 1.700 1.700 1.700 1.700 1.700 (Total)100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000100.000 100.000 100.000 Thermal- Acid Value 0.04 0.08 0.12 0.13 0.050.09 0.11 0.13 0.07 0.10 0.82 0.08 stability mgKOH/g Test

TABLE 2 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. 1 23 4 5 6 7 8 9 10 Formulation Base PAG 94.299 94.200 89.300 84.300 — — —— — — (mass %) Oil PVE — — — — 94.299 93.800 89.300 84.300 — — ECP — — —— — — — — 93.800 — POE — — — — — — — — — 93.800 Leakage Detector 2 0.0010.100 5.000 10.000 0.001 0.500 5.000 10.000 0.500 0.500 Acid Scavenger3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 OxygenScavenger 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000Other Additives 1.700 1.700 1.700 1.700 1.700 1.700 1.700 1.700 1.7001.700 (Total) 100.000 100.000 100.000 100.000 100.000 100.000 100.000100.000 100.000 100.000 Thermal- Acid Value 0.22 0.35 0.70 1.15 0.240.55 0.72 1.09 0.63 0.66 stability mgKOH/g Test

The following base oils were used.

PAG: polyoxypropylene glycol dimethyl ether, kinematic viscosity at 100degrees C.: 9.25 mm²/s

PVE: polyvinyl ether, kinematic viscosity at 100 degrees C.: 15.97 mm²/s

ECP: polyvinylether-polyalkyleneglycol copolymer (mole ratio: 1:1),kinematic viscosity at 100 degrees C.: 9.56 mm²/s

POE: polyol ester, kinematic viscosity at 100 degrees C.: 68.5 mn²/s

The leakage detectors shown in Tables are as follows.

Leakage detector 1: naphthalimide compound (GS-1/PAG, manufactured bySpectronix, Corp.)

Leakage detector 2:2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole

Acid scavenger: alpha-olefin oxide having 12 carbon atoms andalpha-olefin oxide having 14 carbon atoms

Oxygen scavenger: alpha-olefin having 16 carbon atoms

Other additives: antioxidant, extreme pressure agent

Evaluation Results

The results in Table 1 show that any of Examples 1 to 10, each typifyinga system in which a lubricating oil composition blended with thenaphthalimide compound (i.e., leakage detector 1) is mixed with arefrigerant, did not experience an substantial increase in acid value,and thus the thermal/chemical stability thereof proves to be high.

On the other hands, the results in Table 2 show that Comparatives 1 to10, in which leakage detectors structurally different from thenaphthalimide compound used in Examples were blended, each experiencedan increase in acid value, and thus the thermal/chemical stabilitythereof proves to be insufficient. The data on References 1 and 2, inwhich no leakage detector is added, shows that the leakage detector 2used in Comparatives considerably lowers the thermal/chemical stabilityof a lubricating oil composition.

It is understood from the above results that even when the presentlubricating oil composition for refrigerating machines blended with thepredetermined additive is used in a refrigerating machine using astructurally unstable refrigerant, the leakage of the refrigerant can bedetected with a long-lasting stability.

1. A lubricating oil composition for refrigerating machines comprising:a base oil; and an additive in a form of a naphthalimide compound,wherein a refrigerant used in a refrigerating machine in which thecomposition is used is unsaturated hydrofluorocarbon (unsaturated HFC)having a GWP of 1000 or less.